Adherent mononuclear leukocytes defend against tumor by mechanisms which are poorly understood. It has recently been shown that preparations of adherent mononuclear leukocytes from the mouse peritoneum contain both macrophages and a newly recognized type of B lymphocyte, the nonphagocytic adherent cell (NPAC). This project will analyze the relative contributions of macrophages and NPAC to the anti-tumor activity of mouse adherent peritoneal cells. Techniques for separating NPAC and macrophages will be refined. The two cells' anti-tumor activity will be correlated with assays for macrophage activation: phagocytosis mediated by the Fc receptor or complement receptor, nonspecific phagocytosis, pinocytosis, plasminogen activator secretion, chemotaxis, and antibacterial activity. Macrophages and NPAC with different degrees of anti-tumor activity will be linked to tumor cells using a variety of antibodies, F(ab')2 reagents, and inhibitors, to study the importance of leukocyte-tumor cell contact via known leukocyte receptors. Macrophages will be linked to nonphagocytizable tumor cells via the Fc receptor to learn if this contact stimulates secretion of H202 and superoxide with an anti-tumor effect. Finally, I will examine ways in which NPAC may enhance certain macrophage functions, and ways in which serum factors from tumor-bearing mice may suppress them.